During 3D interactive editing or modifying of a representation of a scene, an editor (hereinafter, a user) often may desire to move a target object while viewing the movement within the representation of the scene in real-time using a reference virtual camera. For example, in some applications, a user may desire to translate a two-dimensional (2D) object, e.g., artwork, a drawing, and so forth, in a direction normal to the orientation of the 2D plane on which the 2D object is stored. Alternatively, the user may desire to rotate a 2D or 3D object about an axis of rotation that lies within the 2D plane or within the 3D space.
In some instances, the actual amount of translation or rotation may be determined interactively. For example, in some applications, the user may move a slider, observing in real-time or near real-time the resulting change in geometry on the screen of the display device, until the slider reaches a desired location and/or orientation. Disadvantageously, however, there may be situations in which, during translation and/or rotation, an original view direction of a reference virtual camera provides a poor vantage point from which to view the manipulated geometry on the display device. Such problems arise frequently during a “projection” mode, in which the user is rotating or translating a planar object or a planar canvas containing the object, while image data are being “slide projected” onto the reference planar canvas in instances in which the view direction of the reference virtual camera serves as the slide projector's center.
However, because the view direction of the reference virtual camera is typically oriented in a direction normal to the surface of the frontal planar canvas, it may be difficult to gauge with any precision how far the user has moved the object (or a second frontal canvas containing the object) with respect to the reference frontal planar canvas. As a result, providing an additional camera view direction(s) from an auxiliary virtual camera may be useful to users. In short, it may be desirable to selectively provide a camera view direction(s) from an auxiliary virtual camera that is not necessarily normal to the frontal planar canvas, e.g., a side perspective, a top perspective, a front perspective, a rear perspective, and the like. Advantageously, when viewed obliquely from a different virtual camera angle, e.g., a ¾-top or ¾-side view, changes in the projected data on the planar canvas are discernable.